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United States Patent |
6,126,692
|
Robie
,   et al.
|
October 3, 2000
|
Retaining mechanism for a modular tibial component of a knee prosthesis
Abstract
The present invention provides a tibial prosthetic knee component. The
prosthesis includes a tibial tray having a posterior rail and an anterior
rail, and a tibial insert. The tibial insert has a posterior dovetailed
surface matching the posterior rail in the tibial tray, and an anterior
surface matching the anterior rail in the tibial tray. The posterior rail
of the tibial tray and the posterior dovetailed surface of the tibial
insert are curved to provide clearance for the posterior cruciate
ligament. A retaining clip is provided for retaining the tibial insert in
the tibial tray. The clip includes a tab which extends through the tray
into the insert and a resilient holding member remains unloaded when loads
are applied to the knee, reducing the likelihood of dissociation of the
tray and insert.
Inventors:
|
Robie; Bruce H. (Glen Rock, NJ);
Rosenthal; Daniel E. (Millburn, NJ);
Schmidt; Peter Nelson (Ithaca, NY)
|
Assignee:
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New York Society for the Relief of the Ruptured and Crippled Maintaining (New York, NY)
|
Appl. No.:
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104562 |
Filed:
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June 25, 1998 |
Current U.S. Class: |
623/20.32 |
Intern'l Class: |
A61F 002/38; A61F 002/28 |
Field of Search: |
623/20,18
29/243.56
|
References Cited
U.S. Patent Documents
4213209 | Jul., 1980 | Insall et al.
| |
4257129 | Mar., 1981 | Volz.
| |
4298992 | Nov., 1981 | Burstein et al.
| |
4822362 | Apr., 1989 | Walker et al.
| |
4936853 | Jun., 1990 | Fabian et al.
| |
4944757 | Jul., 1990 | Martinez et al.
| |
5007933 | Apr., 1991 | Sidebotham et al.
| |
5071438 | Dec., 1991 | Jones et al.
| |
5137536 | Aug., 1992 | Koshino.
| |
5194066 | Mar., 1993 | Van Zile.
| |
5344460 | Sep., 1994 | Turanyi et al.
| |
5370699 | Dec., 1994 | Hood et al.
| |
5387240 | Feb., 1995 | Pottenger et al.
| |
5405395 | Apr., 1995 | Coates.
| |
5458637 | Oct., 1995 | Hayes.
| |
5609641 | Mar., 1997 | Johnson et al.
| |
5645604 | Jul., 1997 | Schneider et al. | 623/20.
|
5702463 | Dec., 1997 | Pothier et al.
| |
Primary Examiner: Yu; Mickey
Assistant Examiner: Stewart; Alvin
Attorney, Agent or Firm: Darby & Darby
Claims
What is claimed is:
1. A tibial prosthetic knee component comprising:
a tibial tray for replacing a portion of a patient's tibia, said tibial
tray including a dovetailed posterior rail and an anterior rail, said
tibial tray further including a clip tab cutout in said anterior rail and
a support shelf;
a tibial insert having a posterior dovetail matching said posterior rail in
said tibial tray, and an anterior surface matching said anterior rail in
said tibial tray, said tibial insert including a cutout in said anterior
surface; and
a clip for locking said tibial insert to said tibial tray, said clip
including a holding member and a tab spaced from the holding member, said
clip retaining said tibial insert in said tibial tray when said tab is
inserted through said clip tab cutout and into said cutout in said insert,
and said holding member is engaged with said tray, wherein the tray
includes an opening disposed beneath said clip tab cutout, and the holding
member is received in said opening.
2. The tibial prosthetic knee component recited in claim 1, wherein the
opening comprises a recess formed on the bottom of the tray, and the
holding member comprises a deflectable finger formed with an upwardly
extending knob adjacent a distal end of the finger, the knob being sized
for receipt in the recess.
3. The tibial prosthetic knee component recited in claim 1, wherein the
opening comprises a passage formed in the tray which leads to an upwardly
opening recess, and the holding member comprises a deflectable finger
having a downwardly projecting knob adjacent a distal end of the finger,
the knob being sized for receipt in the recess.
4. The tibial prosthetic knee component recited in claim 1, wherein the
opening comprises a generally trapezoidal recess formed in the tray, and
the holding member comprises a pair of deflectable fingers in a generally
V-shaped configuration and sized for receipt in the recess.
5. A tibial prosthetic knee component comprising:
a tibial tray for replacing a portion of a patient's tibia, said tibial
tray including a dovetailed posterior rail and an anterior rail, said
tibial tray further including a clip tab cutout in said anterior rail and
a support shelf;
a tibial insert having a posterior dovetail matching said posterior rail in
said tibial tray, and an anterior surface matching said anterior rail in
said tibial tray, said tibial insert including a cutout in said anterior
surface; and
a clip for locking said tibial insert to said tibial tray, said clip
including a holding member and a tab spaced from the holding member, said
clip retaining said tibial insert in said tibial tray when said tab is
inserted through said clip tab cutout and into said cutout in said insert,
and said holding member is engaged with said tray, wherein the holding
member comprises a pair of spaced apart tines.
Description
BACKGROUND
1. Field of the Invention
The present invention relates generally to orthopedic prosthetic devices
such as implants and artificial joints and, more particularly, to an
improved retaining mechanism for the tibial component of a knee
prosthesis.
2. Description of the Prior Art
The knee joint consists of the bone interface between the distal end of the
femur and the proximal end of the tibia. The tibial-femoral interface is
covered by the patella, a sesamoid bone within the tendon of the
quadriceps on the front of the thigh. This tendon attaches to the tibial
tuberosity and the posterior surface of the patella, and glides over the
femur. The femur has a medial condyle and a lateral condyle which are
substantially smooth and articulate with the medial condyle and lateral
condyle of the tibia. The tibial condyles are slightly cupped to receive
the condyles of the femur.
When the knee joint is damaged, the natural bones may be unable to
articulate properly. In some cases, a prosthetic replacement of the
damaged section is required to restore normal use of the joint and reduce
pain. Typically the entire joint is replaced by a surgical procedure which
removes the ends of the corresponding damaged bones and replaces these
ends with prosthetic implants.
A total knee prosthesis includes patellar, femoral and tibial components
which are intended to replace the mating surfaces of the patient's femur
and tibia. The tibial component very often consists of a metal tray which
is anchored in the patient's tibia and a plastic insert made of a
lubricous plastic material such as ultra high molecular weight
polyethylene. The plastic insert is subject to wear and, therefore, may
need to be replaced with time. Replacement of the insert is simplified if
it is not necessary to remove the part (tray) which is implanted in the
patient's tibia. Over the years, various retaining mechanisms have been
developed for holding or locking the tibial insert to the tibial tray.
U.S. Pat. No. 4,298,992 discloses a well known total knee prosthesis known
as the Insall/Burstein (I-B II) posterior stabilized knee. The I-B II knee
has been in use for over nine years, and in thousand of clinical cases
there has been no reported dissociation of the tibial insert and tibial
tray. In the commercial product, the insert is laterally loaded into the
tray and captured by anterior and posterior rails, each with a dovetail,
which hold the insert in place. A clip passes through the anterior rail
and is held in the tray by two tines that fit in a mating recess in the
tray, below the lower surface of the insert. The clip also has a
protruberence that fits in a recess in the plastic to prevent
medial-lateral motion of the insert relative to the tray.
Unfortunately, this retaining mechanism cannot be used in a total knee
replacement where the posterior cruciate ligament (PCL) is retained
because insertion of the insert would interfere with the intact posterior
cruciate ligament. Current retaining mechanisms for posterior cruciate
ligament retaining total knee replacements are prone to dissociation of
the tibial insert because the applied loads are partially resisted by the
retaining mechanism which therefore is subject to failure.
An object of the invention is to provide an improved retaining mechanism
for the tibial tray of a total knee replacement, including posterior
stabilized and constrained condylar knees.
Another object of the invention is to provide a retaining mechanism for the
tray of the tibial component of a knee prosthesis specially adapted for
use with knee replacements in which the posterior cruciate ligament is to
be retained.
SUMMARY OF THE INVENTION
In accordance with the invention, the tibial component of a total knee
prosthesis includes a tibial tray having upstanding anterior and posterior
rails, with the posterior rail being curved to accommodate the posterior
cruciate ligament. The posterior rail is dovetailed but the anterior rail
is not dovetailed. A plastic tibial insert has a dovetailed posterior
surface which engages the posterior rail of the tray and a nondovetailed
anterior surface which engages the anterior rail of the tray. The
construction is such that during assembly, the dovetail on the insert may
be brought into mating engagement with the dovetail on the tray, and
simultaneously rotated and slid posteriorly until the dovetail is fully
engaged and the anterior surfaces are brought into mutual contact.
The insert is held in place within the tray by means of a retaining element
which includes a tab which passes through the anterior rail into the
insert to retain the insert in its seated position within the tray. In the
preferred embodiment, the retaining element also includes a spring biased
holding element which is received within an opening in the tray to hold
the retaining element in position. Because the holding element is not
subject to loads applied to the knee, the retaining element is not subject
to displacement yet can be easily removed if it should be desirable to
replace the insert.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an isometric view of the tibial components of a total knee
replacement and a retaining mechanism according to the invention;
FIG. 2 is a left side elevational view of the tibial insert and tray with
the insert being rotated into engagement with the tray;
FIG. 3 is a left side elevational view of the tibial insert fully inserted
into the tray;
FIG. 4 is a sectional view taken along lines 4--4 in FIG. 3;
FIG. 5 is a sectional view taken along lines 5--5 in FIG. 3;
FIG. 6 is a sectional view taken along lines 6--6 in FIG. 4 showing the
clip installed and the insert locked to the tray;
FIG. 7 is a left side elevational view of an alternate embodiment of the
locking mechanism of the present invention;
FIG. 8 is a left side elevational view of yet another alternate embodiment
of the locking mechanism of the present invention;
FIG. 9 is a left side elevational view of still another embodiment of the
locking mechanism of the present invention; and
FIG. 10 is a top plan sectional view of the locking mechanism of FIG. 9.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 is an exploded view of the tibial component of a total knee
prosthesis which includes a tibial tray 12, tibial insert 14 and retaining
element or clip 16. The tibial tray 12 includes a fixation stem 20, a
support shelf 22, and an upstanding anterior rail 24 and posterior rail
26. The support shelf 22 has a generally planar top surface 28. As shown
in FIG. 2, the anterior rail 24 includes an outer wall 30 and an inner
wall 32. The posterior rail 26 includes an outer wall 34 and an inner wall
having a dovetailed surface 36. The inner wall 32 of the anterior wall is
not dovetailed.
As used in the specification and claims, the term "dovetailed" is intended
to refer to a surface(s) which is shaped so as to limit simultaneous
movement of an element having a complementary engaging dovetail surface in
two directions. For example, the dovetail surfaces of the insert and tray
prevent removal of the insert relative to the tray in posterior (rearward)
and superior (upward) directions.
The stem 20 projects downwardly from the support shelf and is inserted into
the proximal tibia 37 to form a permanent connection with the tibia 37
(see FIGS. 2 and 3) in a conventional manner.
The support shelf 22 is generally oblong with a curved posterior edge where
the dovetail 36 intersects the planar top surface 28. The posterior rail
26 is curved to define a clearance notch 38 for the intact posterior
cruciate ligament. The top surface 28, inner wall 32 and dovetail surface
36 form a receptacle for receiving the tibial insert 14.
The retaining clip 16 includes a head portion 43, a tab 44 extending from
the head portion 43, and a resilient holding member which, in one
illustrative embodiment, comprises a pair of tines 46a, 46b extending from
head portion 43 beneath tab 44. The anterior rail 24 includes a clip tab
cutout 40 (FIG. 5) configured to receive tightly the tab 44, and a slot 42
which receives tines 46a, 46b of retaining clip 16. The clip tab cutout 40
is aligned with a corresponding cutout 48 in the tibial insert 14 (FIG.
6). The slot 42 is disposed beneath clip tab cutout 40 within the support
shelf 22 and is shaped as shown in FIG. 5 to retain the tines 46a and 46b
in their outwardly biased position.
The resilient engaging member 46 may take many different forms, such as a
single resilient tine, a deformable rectangular insert, and the like,
several of which are described in greater detail below in connection with
FIGS. 7 through 10.
The tibial insert 14 is integrally formed from ultra high molecular weight
polyethylene or a like material having lubricious properties. The tibial
insert 14 (in the illustrated posterior stabilized embodiment) includes a
stabilizing post 50, and a pair of concave depressions 52a, 52b which
receive the medial and lateral condyles of the fermoral component (not
shown).
The tibial insert 14 includes a posterior dovetailed surface 54 which
engages dovetailed surface 36 of posterior rail 26. The posterior
dovetailed surface 54 has a curved shape matching the posterior rail 26 to
provide clearance for the posterior cruciate ligament as discussed above.
At the opposite side, tibial insert 14 has a nondovetailed anterior
surface 56 which blends into a ledge 58 and a chamfered surface 60 as
shown in FIG. 2. The chamfered surface 60 allows the insert 14 to be
rotated into the tray after the dovetailed posterior surfaces 36 and 54
have been engaged.
The tibial component is assembled by first engaging the corresponding
dovetail surfaces 36, 54 as best seen in FIG. 2, and then rotating the
insert 14 until the anterior surface 56 engages inner wall 32 of anterior
rail 24 of the tibial tray 12 with the bottom surface of the insert 14
lying flat against planar surface 28 of support shelf 22 (see FIG. 3). The
retaining clip 16 is then inserted through the anterior rail 24 by
inserting the tab 44 through the clip tab cutout 40 and into the slot 48
in the insert, and by inserting the resilient tines 46a, 46b of the insert
46 into the slot 42. The individual parts of the tibial component may be
sold in a partially assembled condition. For this purpose, the slot 42 may
include notches 42a and 42b in which the protrusions at the ends of tines
46a and 46b can rest. In the partially assembled condition (shown in
dotted lines in FIG. 5), the ends of the tines are received within the
notches 42a. Before the prosthesis is implanted, the surgeon pushes the
clip into its retention position in which the protrusions on the ends of
the tines 46a and 46b rest within the notches 42b (shown in solid lines).
Because the tines are retained within the tray alone, loads imparted on
the assembly which tend to dissociate the insert 14 from the tibial tray
12 are only reacted to by the tab 44, which transfers the load to the
anterior rail 24 via cutout 40. The load is not transferred to the tines
46a, 46b which hold the retaining clip in place. This configuration
provides greater structural integrity and reduces the risk of dissociation
to the prosthesis.
Referring to FIG. 7, there is shown an alternate embodiment of the
retaining element 70, which includes a clip 72 comprising a tab 74
extending from a head portion 76, the tab being configured for extension
through a tab cut-out 78 formed in tray 80 and a corresponding cut-out in
the tibial insert, similar to the embodiment described above. The clip
further includes a holding element in the form of a deflectable finger 82
disposed beneath the tab and extending outwardly from the head portion.
The finger is downwardly deflectable to clear the bottom of the anterior
rail of the tray as the clip is inserted into the tray. The finger
includes an upwardly projecting knob 84 at the distal end of the finger
that is sized for receipt in a complementary, downwardly opening notch 86
formed on the bottom of the tray.
FIG. 8 shows yet another embodiment of the retaining element, including a
clip 90 comprising a tab 92 and finger 94 with a downwardly projecting
knob 96 at the distal end of the finger. The finger is configured for
extension through a passage 98 formed in a tray 100, with the knob
received in an upwardly opening notch 102 formed in the support shelf 104
of the tray.
FIGS. 9 and 10 show still another embodiment of the retaining element. A
clip 106 includes a tab 108 and a generally V-shaped holding element 110
comprising a pair of resilient fingers 112 angled outwardly from the head
portion of the clip (FIG. 10). The tray 114 includes a generally
trapezoidal recess 116 in the anterior rail 118 of the tray. The recess
includes a relatively small opening which leads to a larger opening inside
the tray body (FIG. 10). The opening is configured such that the fingers
are deflected inwardly as the clip is inserted into the tray. Once the
fingers are inside the recess, the fingers spread outwardly to assume
their unbiased configuration, with the opening maintaining the holding
element within the recess.
Thus, it will be apparent that the locking mechanism of the present
invention may take many different forms and may be used with variously
configured trays and inserts.
The present invention has been shown and described in what are considered
to be the most practical and preferred embodiments. It is anticipated,
however, that departures can be made therefrom, and that obvious
modifications will be implemented by persons skilled in the art.
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